Methods and apparatus for electric motor controller protection

Abstract

A method for monitoring input power to an electronically commutated motor (ECM) is described. The method includes determining, with a processing device, an average input current to the motor, the average input current based on a voltage drop across a shunt resistor in series with the motor, measuring an average input voltage applied to the motor utilizing the processing device, multiplying the average input current by the average voltage to determine an approximate input power, and communicating the average input power to an external interface.

What is claimed is: 
     
       1. A method of protecting a motor controller of an electric motor, said method comprising:
 determining, with a processing device, an average input current to the motor based on a voltage drop across a shunt resistor in series with the motor by integrating the voltage dropped across the shunt resistor with respect to time using an integrator and apply the integrated voltage to an analog-to-digital converter; and 
 measuring at least one voltage; 
 determining, with the processing device, an average input voltage applied to the motor based on the at least one measured voltage; 
 multiplying the average input current by the average input voltage to determine an average input power; and 
 setting a maximum power limit for the motor controller based on the average input power. 
 
     
     
       2. A method in accordance with  claim 1 , further comprising maintaining the average input power below the maximum power limit. 
     
     
       3. A method in accordance with  claim 2 , wherein maintaining the average input power below the maximum power limit comprises controlling the amount of current delivered to the motor. 
     
     
       4. A method in accordance with  claim 3 , wherein controlling the amount of current delivered to the motor comprises pulse width modulating at least one power switch included in an inverter coupled to the motor. 
     
     
       5. A method in accordance with  claim 1 , further comprising using the determined average input power as an indication in an airflow delivery system to control the amount of power delivered to a fan. 
     
     
       6. A method in accordance with  claim 1 , further comprising using the determined average input power as an indication in an airflow delivery system to control the amount of power used by the system. 
     
     
       7. A method in accordance with  claim 1 , wherein determining an average input voltage applied to the motor based on the at least one measured voltage comprises:
 rectifying and filtering an alternating current (AC) input voltage applied to the motor; 
 proportionally voltage dividing the rectified and filtered AC input voltage to a level compatible with an analog-to-digital converter; and 
 averaging multiple readings of the divided voltage over a fixed time interval to determine the average input voltage. 
 
     
     
       8. A method in accordance with  claim 1 , wherein determining an average input voltage applied to the motor based on the at least one measured voltage comprises:
 proportionally voltage dividing a direct current (DC) input voltage to a level compatible with an analog-to-digital converter; and 
 averaging multiple readings of the divided voltage over a fixed time interval to determine the average input voltage. 
 
     
     
       9. A method in accordance with  claim 1 , wherein determining an average input current to the motor comprises applying the voltage dropped across the shunt resistor to an analog-to-digital converter. 
     
     
       10. A method in accordance with  claim 1 , wherein:
 integrating the voltage dropped across the shunt resistor comprises averaging the voltage drop across the shunt resistor according to: −1/RC∫vdt, where “v” is the voltage across the shunt resistor and “RC” is the time constant of the integrator; and 
 applying the integrated voltage to an analog-to-digital converter comprises amplifying the output of the integrator to provide a proper voltage level for an input of the analog to digital converter. 
 
     
     
       11. A method in accordance with  claim 1 , further comprising communicating the average input power to an external interface. 
     
     
       12. A method in accordance with  claim 11 , wherein communicating the average input power to an external interface comprises transmitting the average input power to at least one external device via a digital serial interface. 
     
     
       13. A method in accordance with  claim 12  wherein the average input power is transmitted upon request from an end user I/O device. 
     
     
       14. An electric motor comprising:
 a rotor; 
 a plurality of windings for causing a rotation of said rotor; and 
 a motor control circuit comprising: 
 a switching circuit operable to selectively couple said windings to a power source; 
 a shunt resistor in series with said switching circuit; and 
 a processing device programmed to: 
 determine an average input current to said motor based on a voltage drop across said shunt resistor by integrating the voltage dropped across said shunt resistor with respect to time using an integrator and apply the integrated voltage to an analog-to-digital converter; 
 determine an average input voltage applied to said motor based on at least one voltage measurement; 
 multiply the average input current by the average input voltage to determine an average input power; and 
 set a maximum power limit for said motor control circuit based on the average input power. 
 
     
     
       15. An electric motor in accordance with  claim 14 , wherein said processing device is further programmed to maintain the average input power below the maximum power limit by controlling the amount of current delivered to said motor. 
     
     
       16. An electric motor in accordance with  claim 14 , wherein said processing device is further programmed to use the determined average input power as an indication in an airflow delivery system to control the amount of power delivered to a fan. 
     
     
       17. An electric motor in accordance with  claim 14 , wherein said motor control circuit further comprises at least one analog-to-digital converter coupled to said processing device, wherein to determine the average input current, said processing device is programmed to apply the voltage dropped across said shunt resistor to said analog-to-digital converter. 
     
     
       18. An electric motor in accordance with  claim 14 , wherein to integrate the voltage drop across said shunt resistor, said processing device is programmed to:
 integrate the voltage drop across said shunt resistor according to: −1/RC∫vdt, where “v” is the voltage across said shunt resistor and “RC” is the time constant of said integrator; and 
 apply the integrated voltage to said analog-to-digital converter by amplifying an output of said integrator to provide a proper voltage level for an input of said analog-to-digital converter.